Everyone knows sugar-rich, fatty foods are unhealthy, but we keep eating them. The diet industry is booming, but so are waistlines. In the UK, 1 out of 5 adults is obese; in the US, the figure is 1 of every 3 adults. Why don’t we eat better? Are we just too weak-willed? Maybe not. The picture emerging from recent research into the neurobiology of eating tells a different story, in which our evolutionary history and changing environment have created a dangerous new relationship with our food.

We like the taste of sugars and oils because they’re rich in energy. Foods with a high concentration of them are a valuable energy source, so our ancestors evolved a preference for them. It’s not just a question of taste, though. Rich foods also trigger the release of dopamine, a neurotransmitter involved in our brain’s reward system, which makes us seek them out. It makes sense — after all, rich foods get you more energy for the same amount of effort, which is great when you’re out foraging. The catch, though, is that the whole system — and its controls — evolved in an environment where these kinds of foods where uncommon. Nowadays, energy-packed foods full of sugars and fats are cheap and ubiquitous, a change that’s played havoc with our reward system.

In a 2005 paper entitled “How Can Drug Addiction Help Us Understand Obesity?”, Nora Volkow and Roy Wise summarized a raft of data showing that food and addictive drugs activate the same reward circuitry. In both cases, consistent over-stimulation of the circuit weakens its response, creating the need for a stronger stimulus and leading to the compulsive behaviour we call addiction. The duo argued that drug addiction provides a useful framework for understanding how we eat, writing: “Although each condition has its own interface with brain mechanisms of motivation, the motivational mechanisms themselves largely overlap. […] The guidelines for prevention and treatment of the two disorders are remarkably similar, and some of the same pharmacological interventions that are promising for the control of drug intake are also promising for controlling the intake of food.”

More recently, research by Paul Johnson and Paul Kenny showed that rats fed a so-called “cafeteria diet” (bacon, sausage, cheesecake, and chocolate) showed changes similar to those seen in rats addicted to drugs. Like drugs, the rich diet increased the rats’ reward threshold, making it harder for them to get satisfied. The higher threshold was a result of the rats having fewer dopamine receptors, which is also the case in humans addicted to drugs. Since there are fewer receptors, more dopamine is needed to activate the reward signal, which takes more stimulus — food or drugs. Scientists have also discovered that obese humans tend to have a lower density of dopamine receptors.

Rats fed a cafeteria diet didn’t just show neurological changes; they also kept eating even when exposed to a light that they had been trained to associate with an electric shock. Rats addicted to cocaine also ignored risks to get their reward, while those fed only ordinary chow gave up their food in order to avoid the light. To me, one of the most striking findings was how long it took the reward circuitry to recover when the rats were taken off the cafeteria diet. The reward system recovers in about 48 hours in rats coming off a cocaine addiction, but it took at least two weeks to get back to normal after over-eating.

It’s important to realize that the effect of rich foods on the reward circuit isn’t because of their taste. Mice prefer sugar over the artificial sweetener sucralose even though sucralose is 600 times sweeter. In fact, mutant mice which can’t taste sweet food still like sugar better. This is because sugar, unlike sucralose, activates the dopamine pathway in the reward circuit, which acts together with the taste to create a preference — or an addiction. Last year, a team of scientists identified the neurons that release dopamine in response to sugar. They genetically engineered mice in which these neurons could be activated with a pulse of laser light, and then showed that activating them while the mice ate sucralose made them prefer the artificial sweetener. By contrast, mice engineered to lack these neurons altogether showed no preference between sugar and sucralose.

So what does all this mean? Basically, our reward system evolved to encourage us to seek out rich foods, but it’s getting short-circuited by the overabundance in our environment these days. It’s the same short-circuit that happens in drugs users, and it leads to the same outcome — addiction (in this case, to fatty, sugar-rich foods).

This post strays a bit from the usual purview of Inspiring Science, but I feel like it’s worth writing about and discussing. Many people may not have heard about this research, which is something we can fix together. Hopefully that will help change the conversation about obesity and diet, and the relationship we have with food. I’ll forego my usual flowery ending and instead close with a quote from the Volkow & Wise paper: “Few fields seem to offer as much potential for cross-fertilization as the fields of addiction and obesity research.”

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11 thoughts on “Why you can’t stop – Eating & Addiction”

It appears you missed the last bit of your fifth paragraph, but I’m sure most of us get the gist: food addiction is harder to recover from that a drug addiction.

NPR does quite a few pieces about obesity, so much of this is not new to me (or, at least, not surprising), but what always strikes me is how much the words we use to describe how we eat supports this.

For years now, to explain to people whom have expressed mild disbelief that I don’t drink or use stimulants (illegal or legal), I’ve said, “Food is my drug.”

And it is!! I’m one of the many obese Americans out there struggling with their weight. My husband is a recovered alcoholic, and we try to use the same strategies with food that he’s successfully used with alcohol. Out of sight, out of mind works (somewhat) for me. A support network is needed as well.

The genetically altered dopamine pathway is interesting. Makes me think that maybe they can ‘fix’ me…

I think using strategies for alcoholism to deal with food is a great idea, which is part of why I think it’s important for people to understand how addictive food can be. I also help that increased awareness about that will change how we interact with each other about food and obesity. I hope most people wouldn’t offer an alcoholic a drink because “you deserve a treat”, but we do that with people who are trying to control their diet all the time. From what I’ve read, I think that should change.

I think that there’s such a stigma around obesity in America – people view it as the result of a weak will or laziness – despite all the science that suggests otherwise. I think – like drugs – difficult periods of emotional turmoil often drive us to chase those highs we can get through food. And unfortunately, once you’ve started on this path, it’s very difficult to retrain your brain and body.

The sad things is, food addiction can never be treated the same way drug addiction is because we can never entirely abstain from food. Really interesting article. Thanks for sharing 🙂

I agree that there’s often an unhelpful attitude around food and obesity. I’m not sure that I agree that food can’t be treated like drugs. After all, society doesn’t mandate total abstention from drugs — alcohol and tobacco are legal, but regulated. Stronger regulations around labelling and availabity of food — especially junk food to/for children — could help.

While growing up, I do think I was addicted to food, I was always thinking about chocolate croissans and well, all the pastry. Also, I could buy them in my school. I was an overweight teenager, and this weight just kept on going up. Hopefully I started to get informed, about a year ago went into a plant based diet, and I am now with a normal weight for my age and height. It took me 3 years for this to happen – and it was not a straigh-line easy accomplishment. I do believe that the most important step in being in control of ones nutrition is to seek knowledge, thank you for sharing this and raising awareness. It can be very hard not understanding why a craving is there, and it is very useful to have access to this information.